1. Field of the Invention
The present invention relates to a radio frequency identification (RFID) tag, an information reading apparatus that reads information stored in the RFID tag, and an information reading system that includes the RFID tag and the information reading apparatus.
2. Description of the Related Art
Recently, RFID tags are widely used in a distribution field. The RFID tag is an integrated circuit (IC) chip that stores various kinds of data. A data communication is performed together with a reader/writer that reads and writes data using an electric wave (for example, see Japanese Patent Application Laid-Open No. 2000-272723).
The RFID tag is often used to inspect a quantity of products (the number of products that are received and shipped) and a quality of products (good or bad). For example, the RFID tag is attached to each product, and the quantity is checked based on the number of RFID tags from which data can be read. Furthermore, the RFID tag is attached to each group of products, thereby managing the products by types of products or by modes of packaging.
However, when RFID tags attached to products of different groups are present in a mixed state, an information reading apparatus that reads information stored in the RFID tags cannot identify a product group to which each RFID tag belongs, unless the information reading apparatus has information on an identifier of each of the RFID tags (child tag) attached to each product and information on a group to which the product belongs. Therefore, the information reading apparatus cannot recognize the quantity of products per group, and inspection of the products cannot be performed.
To solve this problem, separately from the RFID tag attached to each product, a group RFID tag (parent tag) is attached to a corresponding product group in which the products are classified. The group RFID tag stores identification information of the RFID tags. The information reading apparatus first reads the identification information of the RFID tags from the group RFID tag, thereby identifying products belonging to each product group.
As explained above, according to the conventional technique disclosed in Japanese Patent Application Laid-Open No. 2000-272723, in the inspection of the products, it is necessary to first read the information stored in the group RFID tag to obtain the identification information of the RFID tag of each product.
However, in the above conventional technique, the group RFID tag cannot be identified automatically from among the RFID tags and the group RFID tags that are present in a mixed state. Therefore, when the RFID tag and the group RFID tag are mixed, an operator must arbitrarily choose the group RFID tag to be read. Specifically, it is required that the operator brings the reader/writer close to the group RFID tag, or a reading range of the reader/writer is narrowed such that the reader/writer reads only the group RFID tag.